With funding from the Health Effects Institute, a non-profit foundation jointly supported by the U.S. Environmental Protection Agency and vehicle manufacturers, we have conducted a prospective cohort study of nitrogen dioxide (NO2) exposure and respiratory symptoms and illnesses during the first 18 months of life. Between January, 1988 and June, 1990, 1,315 infants were enrolled and then followed with collection of daily respiratory symptom data and serial monitoring of NO2 concentrations in their homes. The full protocol was completed by 823 subjects and a total follow-up experience of over one-half million days was accumulated. Follow-up ended in December, 1991 and analyses related to the study's principal focus, the health effects of NO2 will be completed and presented during the fall of 1992. The Health Effects Institute is providing funding through December 31, 1992, but will not support analyses of aspects of the data not directly related to NO2. This small grant application requests funding to utilize fully the resource provided by this large cohort study. This application requests support for analyses directed at the following: 1) Time spent in day-care and the incidence and severity of respiratory illnesses; 2) Breast-feeding and the incidence and severity of respiratory illnesses during the first six months of life; 3) Determinants of wheezing and wheezing illnesses; 4) Determinants of a physician-diagnosis of asthma; 5) Exposure to woodsmoke and incidence and severity of respiratory illnesses; 6) Household demographics, including ethnicity, and incidence and severity of respiratory illnesses; 7) Determinants of the duration of respiratory illnesses; 8) The validity of retrospective parental reports of respiratory illness; 9) Parental perceptions of the risks of indoor and outdoor air pollution; 10) Clinical findings on assessment of ill children in the community.